Leakage Control

Leaks are the major component of water loss in developed countries. This is not always true for developing countries, but it remains an important factor of water wastage. Illegal connections, metering and accounting errors as well as pricing issues should be addressed in priority, but leakage control remains an effective tool for limiting water losses.

A water system includes intakes, water pipelines, storage reservoirs and pumps. Once the water enters the system at the intakes from the source, pumps provide energy to convey the water through the pipelines to storage reservoirs from which it is distributed to consumers. Pipelines are formed of multiple pipes with joints and leakage generally occurs where the pipe joints are faulty or where defects develop in the pipe body. The longer leaks remain unattended the larger the economic and resource loss will be to the authorities, as electric power to run the pumps and chemicals to treat water are also wasted. Pressure in mains, water hammers, soil instability, corrosion of water pipes, poor quality of fittings, traffic loading, age of components are some of the main factors affecting leakage. Leakage control work involves the following major step.

Leakage control work involves the following major steps:

• Preparatory work: updating maps, databases of consumer connections, residing population, water mains, valves and fire hydrants etc.; planning of activities.
• Test for loss assessment and locating the defects (leak detection).
• Repair and replacement of system components.
• Re-assessment, several times if needed.
• Program monitoring.
• Build up procedures and standardised activities applied to the considered system.
• Training of staff, including training of trainers and updating.

Major leaks can be visible on the surface: these have to be fixed in priority. It is the first and most import step of leaks control in developing countries. Purchasing leak detection instruments is an approach typical of developed countries, but not necessarily the most adapted one for developing countries (FARLEY 2001, MCINTOSH 2003). Leakage assessment uses various techniques such as district and/or wastage metering, pressure control, sounding or passive leakage control for continuous supply. For intermittent supply, the mobile tanker, stop tap, or district meter methods as well as pressure, sounding or passive leakage controls can be used. The selection of a method has to be based on local conditions and resources (see also FARLEY 2001 for the description of most methods and their applicability).

It is common in continuous supply systems to measure district flow at night and find a minimum, known as “minimum night flow”. For cost-effective work, district metering is typically done for 2000 to 5000 properties; waste metering is typically done for about 1000 to 3000 properties. These methods are now well established and have been well documented. However, specific reference books / manuals need to be consulted for the adaptation of these methods to intermittent supply.

Using electronic instruments, noise detection principles can be applied by listening to the pipelines and filtering external noises, amplifying the leak-noise of certain frequency range to detect and pin-point the leaks. Advanced state-of-the-art instruments such as electronic sounding rods, multi-frequency leak locators, leak noise correlators or noise loggers also exist. Depending on the chosen technique, instruments may be combined. For continuous supply systems properly metered (usually those of developed countries), software packages such as ‘BABE’ (Burst & Background Estimates) help assessing the annual volume lost for different categories of leaks, depending on their average duration.

For intermittent supply systems, the mobile tanker method has been developed. A small main stretch (typically 100 connections and 400 to 500 meters) is isolated and fed under pressure during non-supply hours, long enough to measure leak flows and locations. Boundary valves and consumer connections are closed. The line supplying the injection point from the tanker contains a meter with a pulsehead, a pressure transducer and a data logger that records pressure and flow (FARLEY & TROW 2003; CPHEEO 2005). A direct measure of leakage, otherwise difficult to locate during short supply hours, can be obtained. The method has been used at large scales in the metropolitan cities of Chennai, Hyderabad, Ahemdabad (India) and Kathmandu (Nepal).

The mobile tanker method is one of the most cost-effective methods: it requires little material and manpower, and does not need installed consumer meters or district meters. Work does not need to be repeated as small stretches are isolated for testing purpose and all defects can be found and repaired within each part.

Another method for intermittent supplies is the stop tap method (adapted from FARLEY 2001): boundary valves and customer's connections stop taps are closed. A special supply is arranged from the nearest water distribution station, and the water flow is directly metered through the test area. Basic leak detection equipment is then used to locate the leak points. The main problem with this method, as compared to the mobile tanker method, is the need to divert water supplies to the test area. It also wastes a lot of water, lost at the leak points during the test, and has to be repeated as only a few leaks are detected each time.

Leakage control is a regular maintenance activity and needs to be given priority, and to be included in the routine maintenance activities by establishing a separate department dedicated to it. Reporting by this department should also include the cost of water saved and the cost of the implemented program. Zonal caretakers reporting to O&M (see also water distribution and water purification) supervisors can be efficient in the follow-up of water leaks and other losses, if familiar enough with the water network and the inhabitants of each zone (MCINTOSH 2003).

In intermittent supply systems, leak points become likely entrances for contamination as pipelines are not under pressure outside supply hours: locating leaks and repairing them helps closing the contamination-prone areas of the water pipeline network and improves the safety of the water.